Sitting alone in her room on the 14th floor of a Chicago hospital, Sharon Hart needed some cheering up.

A week earlier the 48-year-old was shocked to learn what she thought was the stomach flu was actually Acute Myloid Leukemia - blood cancer.

She was subsequently rushed into chemotherapy and has been sick in hospital since.

So when her 14-year-old son, William, called the phone in her room at the weekend, it was a case of great timing.

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Behind the snowy rooftop message that's been cheering up patients at a Chicago hospital is an incredibly sweet son who wanted to make his sick mother smile

Sweet kid: William Hart explains in a TV interview how he and his father used their feet to scrawl the huge message in the freshly-fallen snow

Frightening: Sharon Hart thought she was sick with the stomach flu, however it turned out to be cancer. Although her life has since been turned upside down, the love of her family is getting her through it